Deferred Revenue-Right-to-use contracts and Deferred commission expense - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Movement in Deferred Revenue [Roll Forward]
Deferred revenue - right-to-use contracts, as of January 1	$ 74,174	$ 68,673
Right-to-use contracts current period, gross	2,797	3,081
Revenue recognized from right-to-use contract upfront payments	(2,024)	(1,934)
Right-to-use contract upfront payments, deferred, net	773	1,147
Deferred revenue - right-to-use contracts, as of June 30	74,947	69,820
Movement in Deferred Costs [Roll Forward]
Deferred commission expense, as of January 1	28,589	25,251
Deferred commission expense	1,142	1,239
Commission expense recognized	(829)	(684)
Net increase in deferred commission expense	313	555
Deferred commission expense, as of June 30	$ 28,902	$ 25,806